Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity. Atrial fibrillation is a common sustained cardiac arrhythmia and a major cause of stroke. This condition is perpetuated by reentrant wavelets propagating in an abnormal atrial-tissue substrate. Various approaches have been developed to interrupt wavelets, including surgical or catheter-mediated atriotomy. Prior to treating the condition, one has to first determine the location of the wavelets. Various techniques have been proposed for making such a determination, including the use of catheters with a mapping assembly that is adapted to measure activity within a pulmonary vein, coronary sinus or other tubular structure about the inner circumference of the structure. One such mapping assembly has a tubular structure comprising a generally circular main region generally transverse and distal to the catheter body and having an outer circumference and a generally straight distal region distal to the main region. The tubular structure comprises a non-conductive cover over at least the main region of the mapping assembly. A support member having shape-memory is disposed within at least the main region of the mapping assembly. A plurality of electrode pairs, each comprising two ring electrodes, are carried by the generally circular main region of the mapping assembly.
In use, the electrode catheter is inserted into a guiding sheath which has been positioned a major vein or artery, e.g., femoral artery, and guided into a chamber of the heart. Within the chamber, the catheter is extended past a distal end of the guiding sheath to expose the mapping assembly. The catheter is maneuvered through movements that include deflection of a distal portion of the catheter so that the mapping assembly is positioned at the tubular region in the heart chamber. The ability to control the exact position and orientation of the catheter and also the configuration of the mapping assembly is critical and largely determines how useful the catheter is.
Viewing of the catheter distal tip during a mapping and/or ablation procedure is a major benefit. In particular, being able to see a shaft of the catheter in relation to the distal tip would allow the operating physician to understand catheter orientation in relation to the other catheters found in the same region or chamber of the heart. U.S. Pat. Nos. 5,391,199, 5,443,489, 6,788,967 and U.S. Pat. No. 6,690,963 to Ben-Haim, whose entire disclosures are incorporated herein by reference, describe systems wherein the coordinates of an intrabody probe are determined using one or more field sensors, such as a Hall effect device, coils, or other antennae carried on the probe. Such systems are used for generating three-dimensional location information regarding a medical probe or catheter. Preferably, a sensor coil is placed in the catheter and generates signals in response to externally applied magnetic fields. The magnetic fields are generated by three radiator coils, fixed to an external reference frame in known, mutually spaced locations. The amplitudes of the signals generated in response to each of the radiator coil fields are detected and used to compute the location of the sensor coil. Each radiator coil is preferably driven by driver circuitry to generate a field at a known frequency, distinct from that of other radiator coils, so that the signals generated by the sensor coil may be separated by frequency into components corresponding to the different radiator coils.
It is known to provide the three radiator coils in a biosensor that is carried in a distal tip section of a catheter. Where the catheter has a distal tip with a 2-dimensional or 3-dimensional flexible configuration with shape-memory, the biosensor is typically carried proximally of the configuration for a number of reasons, including the fragile nature of the biosensor and the lack of space in the configuration. However, because the biosensor is not carried on the configuration, a certain amount of human guesswork and/or proximation by the mapping and localization system is applied to determine the location and position of the configuration.
Accordingly, a desire exists for a catheter that can provide more accurate signals of the location of its distal end, especially where the distal end includes a 2- or 3-dimensional configuration with shape-memory.